feat: embed images as base64 data URIs in HTML report

Replace relative file paths with inline base64 data URIs so the HTML
report is fully self-contained. Images now render in GitHub's artifact
viewer (archive: false), offline, and when emailed.

Also:
- Fix typo: jquer-tablesorter → jquery-tablesorter
- Move at_exit outside unless guard (always register)
- Rename artifact to snap_diff-report.html

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: pftg

docs/configuration.md

@@ -224,7 +224,7 @@ Capybara::Screenshot::Diff.color_distance_limit = 42
 
 ### Allowed shift distance
 
-Sometimes you want to allow small movements in the images.  For example, jquer-tablesorter
+Sometimes you want to allow small movements in the images.  For example, jquery-tablesorter
 renders the same table slightly differently sometimes.  You can set set the shift distance
 threshold for the comparison using the `shift_distance_limit` option to the `screenshot`
 method:

lib/capybara_screenshot_diff/reporters/html.rb

@@ -1,5 +1,6 @@
 # frozen_string_literal: true
 
+require "base64"
 require "erb"
 require "fileutils"
 require "pathname"
@@ -68,24 +69,26 @@ def failure_entry_for(name, compare)
         difference = compare.difference
         {
           name: name,
-          original: relative_path(compare.base_image_path),
-          new: relative_path(compare.image_path),
-          base_diff: relative_path(compare.reporter.annotated_base_image_path),
-          diff: relative_path(compare.reporter.annotated_image_path),
-          heatmap: relative_path(compare.reporter.heatmap_diff_path),
+          original: image_data_uri(compare.base_image_path),
+          new: image_data_uri(compare.image_path),
+          base_diff: image_data_uri(compare.reporter.annotated_base_image_path),
+          diff: image_data_uri(compare.reporter.annotated_image_path),
+          heatmap: image_data_uri(compare.reporter.heatmap_diff_path),
           diff_level: difference.ratio && (difference.ratio * 100).round(2),
           area_size: difference.region_area_size,
           max_color_distance: difference.meta[:max_color_distance]&.round(1)
         }
       end
 
-      def relative_path(path)
+      def image_data_uri(path)
         return unless path
 
         pathname = Pathname.new(path).expand_path
         return unless pathname.exist?
 
-        pathname.relative_path_from(@report_dir.expand_path).to_s
+        ext = pathname.extname.delete_prefix(".")
+        mime = (ext == "webp") ? "image/webp" : "image/png"
+        "data:#{mime};base64,#{Base64.strict_encode64(pathname.binread)}"
       end
 
       def write_report
@@ -98,6 +101,10 @@ def write_report
 
 unless CapybaraScreenshotDiff.reporters.any?(CapybaraScreenshotDiff::Reporters::HTML)
   CapybaraScreenshotDiff.reporters << CapybaraScreenshotDiff::Reporters::HTML.new
+end
+
+unless defined?(@_snap_diff_at_exit_registered)
+  @_snap_diff_at_exit_registered = true
 
   at_exit do
     CapybaraScreenshotDiff.reporters.each do |reporter|